The ballistic coefficient (bc)

The 'ballistic coefficient' or bc is a measure
for the drag experienced by a bullet moving through the atmosphere, which
is widely used by manufacturers of reloading components, mainly in the
US. Although, from a modern point of view, bcs are a remainder of
the pioneer times of exterior ballistics, ballistic coefficients have been
determined experimentally for so many handgun bullets, that no treatise
on exterior ballistics would be allowed to neglect it..

The bc of a test bullet bctest moving at velocity
v
is a real number and defined as

the deceleration due to drag of a "standard" bullet
devided by
the deceleration due to drag of the test bullet.

The standard bullet is said to have a mass of 1 lb (0.4536 kg) and a
diameter of 1 in (25.4 mm). The drag coefficients of the standard bullet
can be derived from the G1-function given in literature
and will be named cDoG1(Ma) .
Using

cDotest(B,Ma)
= iDtest(B)
* cDoG1(Ma)

one finds for the bc (assuming "standard" atmosphere conditions)

bctest=1 / iDtest(B)
* mtest/ d2test

This formula also shows that the bc and the form factor iD
of a "test" bullet are two aspects of the same principal simplification:
the substitution of the (unknown) particular drag function of a bullet
by the (given) "standard" drag function of the standard bullet (see also
here).